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8-Hydroxyquninoline Mannich base namely 7-diethylaminobenzyl-8-hydroxyqunioline(DEBQ) was synthesized and characterized by elemental analysis and spectral studies. Chelates of DEBQ with manganese(II) and nickel(II) were isolated and structurally  characterized by elemental analysis, electrical conductance, magnetic susceptibility measurement, thermal analysis, IR,UV-Vis, EPR and Mass spectral data. The Mannich base ligand is bidentate and chelates through the phenolic oxygen and the aliphatic tertiary amino nitrogen atoms. Based on the magnetic and electronic spectral data all the MnII complexes are assigned an octahedral geometry and NiII complexes are assigned a tetrahedral geometry. Antimicrobial susceptibility screening of the Mannich base shows that it possesses excellent activity when compared to the standard drugs and the metal complexes studied. Among the chelates, MnII chelate is more potent than NiII  chelate. Thermal analysis of a few compounds shows two stage decomposition patterns.

Leaf and stem extracts of Mentha piperita plant were tested against four bacterial isolates namely: Bacillus sp. (S1), Bacillus sp. (S2), Bacillus halmapalus and Streptomyces sodiphilus, isolated from commercial Spirulina products. The extraction was carried out with solvents such as petroleum ether, acetone, methanol and ethanol. Antibacterial assay revealed that B. halmapalus was highly sensitive to both leaf and stem extracts. Bacillus sp. (S2) and S. sodiphilus was moderately sensitive to all extracts.